1. Field of the invention
This invention relates to a power-driven tool in which a tool bit is mounted in the front end of the tool holder which is rotatably supported in the hammer body. More specifically, this invention relates to such a power-driven tool in which the rotary angle position of a tool bit is adjustable after the tool bit is attached.
2. Description of the Prior Art
Generally, a tool bit attached to the power-driven tool is integrally rotatable with the tool holder by means of a lock mechanism provided in the front of a power-driven tool. Some tool bits, such as chisels, need to be fixed in the tool holder at an appropriate rotary angle position for ease of use. Japanese Patent Application Laying-Open Gazettes Nos. 54-27801 and 61-19395, address such a need. In these prior-art hammer drills, a tool bit is engaged with or disengaged from a clutch member disposed between the tool holder and the output gears for selecting an operation mode from: a drill mode in which only rotation is transmitted to the tool bit; a hammer mode in which only hammer strikes are transmitted; and a hammer drill mode in which rotation and hammer strikes are transmitted at the same time. The tool holder can be placed in an idling position in which the tool holder is disengaged from the clutch member to permit the rotary angle position of the tool bit to be adjusted. Once the tool bit is set to a desired rotary angle position, the tool holder is locked with the clutch member or some other rotation preventive mechanism. This structure is a particularly useful feature when the tool bit is a chisel as it allows the rotary angle position of the tool bit to be adjusted even after it is mounted.
In this structure, however, there is a considerable distance between a sleeve with which to operate the lock mechanism to mount the tool bit in the tool holder and the clutch member with which to place the tool holder in the idle position. This gives rise to the following two problems: poor operability arising from the fact that the mounting of the tool bit and the setting of its rotary angle position must be performed separately by two separate mechanisms disposed remotely from each other and increased cost for providing the two mechanisms required to carry out the bit mounting and the rotary angle setting. Thus, the foregoing configuration is suitable for hammer drills which selectively perform either bit rotation, hammer strikes, or both, but not for power-driven hammers or similar tools designed to perform only one type of operation.